Pore burner and cooking appliance containing at least one pore burner

ABSTRACT

The disclosure relates to a pore burner, especially for cooking appliances, including a housing provided with at least one inlet for a gas/air mixture as a fuel and/or at least one inlet for air and/or at least one inlet for gas and/or at least one outlet for air and/or gas and/or waste gases. The housing includes at least one dimensionally stable, porous molded body formed of sintered metallic powder and/or pressed metallic wire mesh, on the surface of which and/or in the pore spaces of which are reaction zones for the flame development for forming a surface burner. The disclosure also relates to a pore burner including at least one distribution device for the targeted orientation of part of the gas and/or air flow and/or part of the gas/air mixture flow, said distribution device being at least partially arranged and/or molded in the hollow body in such a way that part of the air and/or gas flow or part of the gas/air mixture flow can be distributed such that the inner wall of the hollow body, especially in the region of the distribution device, has a non-homogeneous pressure distribution.

The present invention concerns a pore burner, especially for cookingappliances, with a housing having at least one inlet for gas/air mixtureas fuel and/or at least one inlet for air and/or at least one inlet forgas and/or at least one outlet for air and/or gas and/or exhaust, aswell as a cooking appliance containing at least one pore burner.

The invention also concerns a pore burner system, as well as the use ofpore burners and pore burner systems for heat and/or steam generation incooking appliances and heating appliances, as well as finally thesecooking and heating appliances.

Pore burners are adequately known to one skilled in the art. Thesegenerally involve a burner with a stipulated combustion chamber volumewith spatially connected cavities, through which or in which a definedflame zone is formed. Variants of known pore burners are described, forexample, in U.S. Pat. No. 5,522,723, WO 95/01532, DE 199 39 951 A1 andDE 199 04 921 C2. For example, by means of pore burners the size ofindustrial and household steam and hot water vessels can be reduced,since the heat energy is released both by radiation and by heatconduction so that the convective fraction of heat transfer is reduced.For example, a housing vessel is described in DE 199 04 921 C2 thatincludes a pore burner suitable for heating of liquids, in addition to aradiation heat exchanger and a convection heat exchanger. A large waterspace vessel for generation of steam and/or hot water equipped with apore burner is found in DE 198 04 267 A1.

Especially with a compressed design and high surrounding temperatures,according to DE 199 39 951 A1, a frequently occurring flashback ordeficient flame stability under these conditions, for example, caused bypressure fluctuations and partial vacuum, is avoided by the fact thatthe pore size of the pore burner increases in the direction of flow. Inthis case a critical Peclet number must be maintained for the pore sizein one zone of the porous material, above which flame development occursand below which it is suppressed. In a pore burner as described in DE199 39 951 A1, reaction of the fuel/oxidizing agent mixture occurswithin the porous matrix. This porous matrix is preferably produced bypackings made of temperature-resistant ceramic spheres or saddles.Filler packings according to DE 199 39 951 A1 accordingly have at leasttwo zones of packing material with different pore size. WO 95/01532 alsodeals with the problem of generating a stable flame at low temperatureand low pollutant emission. It can be gathered from this document thatthe porosity of the pore burner is changed along the combustion chamberso that the pore size increases in the flow direction of the gas/airmixture from the inlet to the outlet. The employed porous material ofthe pore burner is again obtained by a packing, for example, in the formof loosely layered grains that are solidified in a sintering process.Finally, basic variants for pore burner technology are described in EP 0840 061 A1 and in DE-OS 2 211 297.

In the pore burners known from the prior art just described, thereactions between the combustion gas and the oxidizing agent underlyingflame formation generally occur mostly or fully within the porousmatrix. The hot reaction products therefore emerge from the burnercavities without flame formation. This procedure means that flames arecooled by the burner material, which helps to prevent further flamepropagation as well as flashback. However, if the burner masses andburner loads are chosen very small, flashback can occur. For example,this is regularly the case, if high temperatures are present in compactheating appliances because of high surrounding temperatures even in thecombustion chamber itself. Flashback can often be reached merely becauseof sufficient flame cooling. However, a large mass with high heatcapacity and good thermal conductivity is required for this. Anothercommon feature of the described pore burner devices is that optimizedgas homogenization and gas distribution over the burner surface, as wellas sufficient flame stability as well as shape stability of the surfaceare regularly achieved only by using several components of differentgeometries and/or materials.

Appropriate flat flame burners based on pore burners have thus far beenknown only in the form of sintered discs, for example, as flat flameburners according to the so-called “Kaskan type” (according to W. E.Kaskan, “The dependence of flame temperature on mass burning velocity”,6^(th) Symposium (International) on Combustion, The Williams & WilkinsCompany, Baltimore, 1956, pages 134 to 143).

A high degree of flame stability, the prevention of flashback andensuring a uniform and constant flame front in a flat flame burner canregularly be obtained only with a porous material of high homogeneity,since otherwise a nonuniform flow profile generally results. A porousmatrix with sufficiently high homogeneity, however, for the most partcan only be implemented up to a stipulated component size. For largerdimensioned burner units, trade-offs with respect to uniform flowprofile and therefore the accompanying properties must thereforeregularly be tolerated.

Ordinary fully premixing burners, especially flat burners and flat flameburners have thus far generally been made from sheet metal provided withholes and/or slit patterns, for example, as known for burners incylindrical combustion chambers. For roughly homogeneous distribution ofthe gas mixture, additional sheets are also required with a coarserperforation, which are situated beneath the aforementioned sheet. Onlywith these design stipulations is it possible to regularly adjust theflow rates so that the corresponding gas/air mixture can be fed to eachsite in the appropriate amount. Known flat burners can also consist of aflexible wire mesh, perforated ceramic or wire fabric fastened to asupport structure. However, for gas homogenization and gas distributionas well as flame stability and shape stability of the surface, thecombination of several components of different geometries and materialsis always required.

Thus far, conventional heating systems with electrical or gas-drivenheating elements have been generally resorted to for cooking appliances.Improving the efficiency of such heating systems would contribute to asaving of natural energy resources and a reduction in pollutantemissions.

It would therefore be desirable to be able to resort to cookingappliances that have a very energy-efficient and low-pollutant andtherefore ecologically efficient heating system, regardless of theirsize.

Pore burners now available are often also characterized by the factthat, when fully premixed gas/air mixtures are used, sharply differingcompositions as well as very variable volume flows can be implemented atlow surface load. Especially when a homogeneous gas mixture is used,very low exhaust emissions are obtained. However, it is also observed inthese pore burners that, when the burner is in the so-called cold stateand the employed gas mixture only has a very low energy content, forexample, with a very high air ratio and/or low heating value of thecombustion gas, ignition by spark ignition often fails. Even when sparkignition occurs under the conditions just outlined, the energyintroduced by the sparks is often only sufficient for local ignition ofthe gas mixture because of the desired stabilization of the reactionzone in the vicinity of the porous material. Liberated heat of reactionis absorbed by the surrounding material so that energy is removed fromthe gas mixture in the ignition zone and the chain branching reactionsrequired for flame formation are suppressed.

The above drawbacks can be more or less avoided by using a strongignition coil with high ignition energy, high ignition frequency and/orby the simultaneous use of several ignition electrodes, but theseexpedients require additional space and result in additional costs sothat the original advantage of pore burners is qualified again. The sameis true, if permanent ignition by means of an auto-igniter or ignitionburner are provided instead of ignition coils or ignition electrodes.

The task underlying the present invention was therefore to make poreburners available for cooking appliances in particular and to modify thegeneric pore burners so that they are no longer burdened with thedrawbacks of the generic pore burners and, in particular, have a highdegree of flame stability and homogeneity, especially when designed asflat burners or flat flame burners. Accordingly, another underlying taskof the present invention was to modify a generic cooking appliance sothat it can be heated with high energy efficiency constantly andefficiently from an ecological standpoint with the lowest possibleoperating costs. Finally, another task underlying the present inventionwas to furnish a pore burner that guarantees improved ignitionregardless of the energy content of the fuel mixture or the condition ofthe pore burner and helps to avoid delayed ignition.

This task is solved according to the invention by pore burners with ahousing having sintered metal powder and/or especially pressed metalwire mesh in the form of at least one dimensionally stable, porousmolded element, on whose surface and/or in whose pore spaces reactionzones for flame development are present to form a flat burner.Accordingly, the entire molded element surface can also represent theoutlet of the pore burner according to the invention, because of theporous structure and optionally also without a defined, large-surfaceoutlet, for example, on one end of the housing. The pore burneraccording to the invention regularly has at least one inlet for agas/air mixture as fuel. In addition or as an alternative, the poreburner or housing of the pore burner can have at least one additionalinlet for air and/or an additional inlet for gas. For example,separately supplied air can be used as secondary air or also for thecooling of components of the pore burner. So-called fully premixingburner systems are used preferably, especially in cooking appliances.

The pore burner according to the invention can be used, for example, forheat and/or steam generation in cooking appliances, especiallygas-heated cooking appliances and also in heating appliances, likeheating vessels or gas heating appliances, for example, in thehousehold, especially when using cylindrical combustion chambers.

The pore burners according to the invention, used in cooking appliances,for example, can represent partially premixing and especially fullypremixing pore burners. In this case the burners can be a cylindricaltube preferably closed on one end. The application of gas outletopenings distributed on the periphery of the tube has also been shown towork.

It can be prescribed according to the invention that the molded elementbe an essentially hollow element, especially a hollow cylinder.Appropriate hollow elements can also have arbitrary geometric shapes,for example, an ellipse, triangle, square, rectangle or any polygon incross section. Appropriate hollow elements can also fully dispense witha defined, large-surface outlet opening and be designed, for example, asan ellipse, sphere or cylinder with only at least one defined openingfor inlet of the gas/air mixture. By using hollow elements it ispossible in a simple manner to create the largest possible surface for auniform flame front.

It has turned out to be very advantageous that pore burners areaccessible, in which the molded elements include at least one mountingand/or fastening element, especially a groove, a tongue, a flange and/ora thread. Mounting and fastening elements can be integrated with thepore burners according to the invention already in the dimensionallystable molded elements, for example, from pressed metal wire mesh, sothat the production costs of the pore burner according to the inventioncan be reduced and production for large series can be implemented muchmore easily. Naturally, the dimensionally stable molded element can alsobe simply welded on for fastening, for example, on the tube to supplythe fuel mixture. This can be achieved in particularly simple fashion,if both the tube and the dimensionally stable molded element havecorresponding cross-sections and the molded element is configuredcylindrical and the tube has a circular cross-section.

Particular advantages with respect to handling and minimization ofcomponents are obtained by the fact that the mounting and fasteningdevice is incorporated directly in the porous molded element material ofthe pore burner. For example, a thread can be made in the pore element.Consequently, no additional mounting or fastening devices and no joiningtechnique for coupling to the pore burner are required.

According to another aspect of the invention, pore burners containing atleast two molded elements lying one against the other in form-fitfashion at least in sections are present, which are connected to eachother in areas, preferably to form a groove. By combining dimensionallystable molded elements in form-fit fashion, large-dimensioned poreburners can also be made without having to tolerate drawbacks withrespect to uniform gas passage or uniform flow profile. Two or moreassembled molded elements can enter into a stable connection via a bevelor groove. It is particularly advantageous if the adjacent moldedelements can be joined or inserted one in the other flush and firmly,for example, via a groove/tongue structure, without requiring additionalfastening devices. However, it can be necessary to permanently fastencoupled molded elements by means of spot welding. The molded elementsare then preferably only joined together at very few adjacent sites andsecured against loosening. A constant material density therefore remainseven in the region of joints so that a uniform flow profile isguaranteed. To the extent that in very large molded elements of theaforementioned type high homogeneity of the porous material andtherefore the most uniform possible flow profile cannot always bemaintained, with the variant just described pore burners of larger sizebecome accessible, which have an extremely uniform flow profile overtheir entire burner surface. In a preferred variant, the dimensionallystable molded elements, especially hollow elements, are designed intheir end regions or head surfaces so that they correspond to each otherin shape so that the front region of one molded element is inserted tofit in the rear region of another molded element, especially one ofidentical design. Pore burners can therefore be obtained that can bearbitrarily extended in length without having to tolerate the drawbackswith respect to homogeneity.

It has therefore turned out to be particularly advantageous that thepore burner according to the invention can be converted as such to astable shape or be present in a stable shape configured so that two ormore such pore burners can be connected to each other. For example,adjacent pore burner segments to be connected to each other can beconfigured on their sections being coupled so that they can be insertedone into the other without requiring additional fastening devices.According to one variant, for example, the open end section of one poreburner segment can be provided with at least one groove that can beconnected to fit with an end section of an adjacent pore burner segmentprovided with at least one tongue. The shape stability of the employedpore burners is then already achieved during production by sintering ofmetal powder and pressing of metal wire mesh without requiringadditional mechanical support elements. Naturally it is possible tocouple not only two pore burners via groove/tongue elementscorresponding to each other, but three or more pore burners or poreburner segments can be coupled to each other by means of theaforementioned joining technique to form a uniform pore burner. The endpiece of this combined pore burner then preferably has a closure, forexample, in the form of porous burner material so that the pore burnerhas no outlet opening. A one-piece pore burner, like a pore burnersegment, can be configured both cylindrically and conically. The sameapplies to a pore burner formed from several pore burner segments. Thepore burner then preferably tapers in the direction toward the end.

It can be prescribed according to the invention that the materialdensities of at least two adjacent molded elements essentiallycorrespond.

It has also turned out in this context to be a preferred variant inwhich the material density in the region of the joining site of twojoined molded elements corresponds especially to the material density ofat least one of these molded elements.

Another embodiment according to the invention is characterized by thefact that the surface of the molded element has at least oneirregularity, especially at least one indentation and/or elevation thatdeviates from the base surface of the molded element.

By means of indentations and/or elevations, i.e. irregularities in thesurface of the molded element, formation of an essentiallytwo-dimensional reaction zone is regularly prevented. Such surfaces,which do not have a continuously uniform surface and therefore uniformlyrepeating structures are preferred accordingly. For this purpose it isgenerally already sufficient to use molded elements, especially hollowelements with different material thicknesses, especially if they arebased on a sintered metal powder. In this way development ofself-induced oscillations on the burner surface is already prevented.The surface of the dimensionally stable, especially pressed metal wiremesh is already sufficiently irregular in general as such in order tosuppress the described resonance phenomenon, but naturally can also havedifferent thicknesses.

As a result, one variant proposes that the wall thickness of one moldedelement be varied and especially that it have at least two differentthicknesses. The wall thickness of one hollow element in this variantdoes not have to be constant within it.

Preferred pore burners according to the present invention are flat flameburners.

Particularly preferred pore burners are characterized by the fact thatthe molded element has a compressed density in the range from about 2.5to about 5 g/cm³, especially about 2.8 to about 4.5 g/cm³, at least inareas, especially in the area of the metal wire mesh. Lower pressdensities generally require lower blower power because of the smallerpressure losses, whereas more uniform reaction zones can be achievedwith higher press densities. The pressed metal wire meshes according tothe invention, just like the sintered metal powder molded parts, arealready stable as such and do not require any stabilizing elements, forexample, in the form of perforated sheets, in order to producefunctionally capable flat flame burners, for example, to provide mixtureguiding or for shaping.

Such pore burners are also advantageous in which the wire diameter ofthe metal wire mesh lies in the range from about 0.1 to about 0.4 mm,especially from about 0.16 to about 0.28 mm. In addition to compresseddensity, the porosity of the pore burner according to the inventionbased on pressed wire meshes can also be influenced by the wirethickness, i.e., the wire diameter and/or the number of pressed wires inthe mesh. For example, if the wire mesh consists only of a relativelythick wire, the pore burner generally has relatively large pores withessentially corresponding pore sizes. If, on the other hand, three wireswith smaller diameters are used, pores of different size are generallyobtained with the same compressed density, which, however, generallylies on the average below the variant just described.

Pore burners according to the invention containing metal wire meshesaccordingly also have, advantageously, 1 to 5, especially 1, 2 or 3metal wires.

It can then be prescribed according to the invention that the metal wiremesh be axially or radially wound before pressing.

Pore burners according to the present invention are also preferred withwhich surface loads in the range from 20 to 300 W/cm², especially from30 to 260 W/cm² are accessible. Accordingly, in the pore burnersaccording to the invention the flame does not go out even at 200 W/cm²or more. The maximum surface load is then often restricted not by thewire mesh but by the feed power of the air and/or gas feed. The surfaceload lower limit is regularly formed by the fact that the flame isextinguished as a result of high heat conduction on contact with themetal surface. With a three-wire metal mesh based on a heat-resistantsteel, for example, 1.4828, with a compressed density of about 3.8 g/m³,surface loads in the range from about 30 to 160 W/cm³ can be achievedwithout difficulty. The pore burner according to the invention thereforepermits a very broad range of possible operating states between flameextinction on the one hand and flame raising on the other, and thereforealso a power modulation range of 1:5 or more. For example, at a surfaceload of about 70 W/cm² with an air ratio of about λ=1.2 an incandescentwire mesh is obtained. During a reduction in air ratio, incandescencewill occur at higher powers and at higher air ratios the surface onlyradiates at very low power. With increasingly more intenseincandescence, the percentage of heat transported by radiation from thereaction zone becomes increasingly larger.

It is proposed in another variant according to the invention that themetal powder and/or metal wire mesh includes at least one metal and/ormetal alloy that forms an oxide layer, especially a metal alloycontaining chromium and/or aluminum. Heat-resistant materials, forexample, heat-resistant steels, are considered appropriate metals andmetal alloys for the metal powders being sintered and especially for thewire mesh. These include, for example, high-alloy steels, likelow-carbon austenitic chromium, nickel and manganese steels. Theheat-resistant steel 1.4828 (X15 CrNiSi 20-12) can be referred to as anexample. Those metal or metal alloys that can form an oxide layer ontheir surface are also readily suited so that the molded articles can beprovided with a protective layer. Particularly appropriate metal alloyshave aluminum and/or chromium fractions or consist of these metals. Anappropriate material, for example, is the alloy with material number1.4767 (CrAl 20 5), as well as alloys with the material number 1.47675.

The task underlying the invention is solved according to another aspectby a pore burner having at least one distribution device for deliberatealignment of one part of the gas and/or air stream and/or the gas/airmixture stream, which can be arranged and/or molded at least in sectionsin the hollow element of the pore burner, so that part of the air and/orgas stream or the gas/air mixture stream can be distributed in a mannerso that the inside wall of the hollow element experiences anonhomogeneous pressure distribution, especially in the region of thedistribution device.

Whereas the gas/air mixture enters the cavity essentially uniformly inordinary pore burner cavities, it is possible in the device according tothe invention to deliberately divert part of the gas/air mixture streamto one region of the inside wall of the pore burner hollow element. Thegas/air mixture is fed to this selected region on the inside wall with astronger pressure than to the surrounding areas of the hollow element.

In a preferred variant it is prescribed that the distribution devicerepresents a baffle plate.

It can then be further prescribed that the distribution device includesessentially metallic and/or ceramic materials and is made, for example,from stainless steel.

The distribution device can be present, for example, in the form of aplate or a three-dimensional structure, for example, a wedge, at leastin sections in the hollow element as long as it is guaranteed that thegas entering the hollow element is diverted partly to one region of theinside wall of the hollow element. The distribution device can be anarbitrarily shaped diversion or deflection structure extendingobliquely, i.e., at an angle, into the hollow element. Naturally, thedistribution device, especially the baffle plate, can have not only adiversion or deflection surface, but be arbitrarily shaped, providedthat mounting and/or the configuration of the distribution devicepermits partial deflection, as just explained, of the enteringcombustion gas. For example, the distribution device or baffle plate canhave a round, oval or angular cross-section. In principle, thecross-sectional shape of the distribution device can always be easilyadjusted to the cross-sectional shape of the pore burner hollow element.The distribution device or baffle plate can also be configured kinked,annular, step-like or bent.

In another embodiment, it has proven advantageous, if the distributiondevice or baffle plate has at least one passage or opening. By usingsuch perforated distribution devices, the amount of gas to be divertedcan be influenced particularly effectively and it can be ensured that asufficient amount of combustion gas always reaches the remaining sectionof the hollow element of the pore burner following the distributiondevice so, that the entire pore space and its surface can be utilizedfor flame formation.

According to a particularly preferred variant, the size of the passagesin the distribution device, especially during pore burner operation, isvariable. In this manner it is possible, for example, to immediatelyreact to changes in composition of the fuel mixture in order toguarantee continuous, uniform flame formation over the entire poreburner.

The pore burners according to the invention can also have at least oneburner tube for air and/or gas that can be connected to an inlet of thepore burner. This burner tube is generally a component of the supplyline.

The distribution device can be present both in sections in the hollowelement and also in the burner tube or be fully present in it or mountedin it.

It can then be prescribed that the distribution device can be fastenedat least in sections to the burner tube and/or hollow element. Generallyit is sufficient if the distribution device is fastened via one or twospot welds on the inside of the burner tube. In this case it has provenadvantageous, if the distribution device has no direct connection to thehollow element.

Another advantageous embodiment is characterized by the fact that thedeflection surface of the distribution device, especially the baffleplate, is sloped relative to the center axis of the hollow element,especially of the hollow cylinder.

In principle, a slight slope, for example, of the baffle plate relativeto the center axis of the hollow element is already sufficient to supplya selected region on the inside surface of the pore burner hollowelement with the fuel mixture in a preferential fashion, i.e., with ahigher pressure. Slope angles in the range from 10 to 45°, especiallyfrom 15 to 30° have proven to be particularly advantageous. Thedistribution device can naturally also have a blade shape or be bent.

Optimal results are then regularly obtained, if the maximumcross-sectional surface of the distribution device in the direction offlow of the gas/air mixture is more than 50%, preferably 55 to 75% ofthe cross-sectional surface of the hollow element in the region of thedistribution device. Appropriately, sufficient combustion gas shouldalways go past the edges of the distribution device and/or pass throughopenings in it into the sections of the pore burner hollow element thatfollow the distribution device.

Another variant according to the invention has pore burner systems asobject, which include at least one feed tube for air and/or gas, whichcan be connected to an inlet of the pore burner, and/or at least oneignition device.

It can then be prescribed according to the invention that at least oneinlet of a dimensionally stable molded element be connected via amounting and/or fastening element, especially a flange and/or a thread,to at least one feed tube and/or burner tube for air and/or gas.

It can also be prescribed according to the invention that at least oneinlet of a dimensionally stable molded element be at least partiallywelded to at least one feed tube and/or burner tube and/or gas.

It can also be prescribed according to the invention that the ignitiondevice be arranged in the region of the outside of the hollow element inthe region on whose corresponding inside the distribution device has thesmallest spacing. The ignition device, for example, ignition electrode,accordingly preferably lies where the diverted combustion gas mixtureemerges from the pore burner wall so that the flame is regularly ignitedwith the first ignition spark. The reaction front continuouslypropagates afterward.

According to another aspect of the present invention, the task is alsosolved by a cooking appliance, especially a gas-heated cooking appliancecontaining at least one pore burner, especially a pore burner accordingto the invention or a pore burner system according to the invention.Those with closed and open systems are considered as cooking appliances.Gas-heated cooking appliances, especially those with a pore burner thatfunctions as a flat burner or flat flame burner are preferably resortedto. The smallest cooking appliances, for example, kitchen cookingappliances can then also be equipped with pore burners, especially poreburners according to the invention just like large cooking appliancesthat are used in large kitchens, for example. Appropriate areas ofapplication for the pore burners according to the invention includesteam cooking appliances or also so-called Combi-steamers.

A very high degree of flame stability is achieved with the pore burnersaccording to the invention. At the same time, flashback is essentiallyfully prevented. Pore burners are therefore provided with a porousmaterial of high homogeneity and uniform flow profile that have auniform and constant flame front as surface burners and are suitable inparticular as flat flame burners. A quasi-two-dimensional flat flame ismaintained over the entire burner surface with the pore burnersaccording to the invention. The cooking appliances according to theinvention have a very high efficiency and can be operated withexceptional ecological efficiency, for example, resource-sparing andlow-pollution. The heat input is then very uniform and can also beprecisely regulated and controlled directly and simply. The propertiesjust described can also surprisingly be implemented with cookingappliances according to the invention that are dimensioned small. Thecooking appliances according to the invention can therefore be used bothin large kitchens, for example, cafeteria operations, and also inrestaurants and guest houses. Cooking appliances with flat burnersaccommodated in them are therefore accessible without difficulty.

The surprising finding that by means of a distribution or guide devicemounted in the internal space of a pore burner hollow element at leastpart of the introduced or blown-in gas/air mixture is deliberately fedto a specific region of the inside wall of this hollow element alsoforms the basis of the present invention. In this way fuel supply can bereliably achieved, which is always sufficient to be ignited with anignition spark. In particular, pore burners can be ignited withoutproblem independently of their initial state and independently of thequality of the gas/air mixture. Because the gas/air mixture emergesoutward within a defined region through the porous hollow element, thereaction can be started and also maintained via an ordinary ignitiondevice mounted in the region of the preferred fuel outlet. The poreburner according to the invention functions without problem and reliablyunder a wide variety of reaction conditions just because of this notvery demanding design expedient. It is also advantageous that notrade-offs need be made with respect to the compact design of the poreburners. It is of particular advantage that the spacing between thesurface of the pore burner and the combustion chamber boundary can bekept very low. This could not be easily achieved with ordinary burnertypes, since increased flow velocities always accompany a reduction inspacing, which thus far has often led to the extinguishing of flames. Inaddition, a persistently high degree of flame stability is achieved andflashback is essentially fully prevented.

Additional features and advantages of the invention are apparent fromthe following description, in which preferred variants of the inventionare explained in detail with reference to the schematic drawings. In thedrawings:

FIG. 1 shows a schematic layout of a cooking appliance according to theinvention containing a pore burner;

FIG. 2 shows a hollow cylindrical pore burner in cross section;

FIG. 3 shows a schematic perspective view of a pore burner according tothe invention;

FIG. 4 shows a schematic cross-sectional drawing of the pore burneraccording to FIG. 3; and

FIG. 5 shows another schematic cross-sectional view of the pore burneraccording to FIG. 3.

The cooking appliance 1 depicted in FIG. 1 includes an internal space 2with a pore burner 4 according to the invention to generate hot air. Asan alternative or in addition, steam can also be generated with the poreburner 4 or an additional pore burner (not depicted). To monitor theburner function, each pore burner 4 has a sensor (not shown) in the formof an ionization current sensor as well as an ignition device (notshown). The pore burner 4 is supplied with combustion gas or acombustion gas mixture via a supply line 6 by means of a first gasfitting (not depicted). This gas fitting assumes the function ofpressure control, amount adjustment and optionally gas filtering. Thepore burner 4 is designed as a hollow cylinder and has a thread on oneend that is integrated in one piece in the molded element forming thepore body (not depicted). The dimensionally stable molded element 7present in this variant as a pressed wire mesh can be screwed directlyto a base 8 via this thread so that a reliable connection with thesupply line 6 is already guaranteed without requiring additionalcomponents, which also makes it possible to exchange different poreburners 4 or molded elements 7 with each other in simple anduncomplicated fashion.

FIG. 2 is a schematic depiction of a pore burner 4′ in cross section.The wall 10 of the hollow cylindrical-shape molded element 7′ of poreburner 4′ has irregularities 12 and 14 in the surface 16 of the moldedelement, which come down to different thickness of the molded elementwall 10. In pore burners according to the invention configured in thisway, the phenomenon of combustion-related, self-induced oscillations nolonger regularly occurs. By designing the irregularities 12 and 14 ofmolded element 7′ as grooves that can engage one in the other,larger-dimensioned pore burners can be created with these moldedelements 7′, which can be positioned one against the other in form-fitfashion. The groove 12 of a first molded element 7′ then engages in thegroove 14 of a second molded element 7′ whose free groove 12 can againbe combined with the groove 14 of a third molded element 7′ with shapemating.

FIG. 3 is an alternative pore burner system 3′ according to theinvention, containing a pore burner 4″ according to the invention with aburner tube 24, a feed tube 26 connected to it, as well as a flange 28connected directly to the feed tube 26. The flange 28 has several screwholes 34 for mounting, for example, in a cooking space of a cookingappliance or in a steam generation unit of a cooking appliance. A mount36 for the ignition source 22 is also mounted on flange 28. The baffleplate 100 extends into pore burner 4″, which is configured in the formof a hollow cylinder. This baffle plate 100 is arranged so that itsupplies part of the gas/air mixture reaching the internal space of poreburner 4″ via the feed tube 26 and burner tube 24 deliberately to adefined region of the inside wall of the pore burner 4″. For thispurpose it is already sufficient, if the baffle plate 100 is slopedrelative to the center axis of the hollow cylindrical pore burner 4″ inthe direction toward the inside wall of this hollow cylinder. Forexample, an essentially rectangularly shaped baffle plate 100, shown inFIG. 3, can extend obliquely into the internal space of the hollowcylinder. If the baffle plate 100 is also present in sections in theburner tube 24 or mounted there in sections, the gas/air mixturearriving via the feed tube is channeled in parts in timely fashion inthe direction toward the desired region of the inside wall of the poreburner. In this manner ignition is possible in an early section of thepore burner body fully without problem. In a preferred variant thebaffle plate 100 can also be arranged moveable or rotatable within thehollow cylinder. For example, during use of a high-energy gas/airmixture, its channeling is unnecessary, since ignition problems need notbe reckoned with, for which reason it would work to align the baffleplate 100 parallel to the center axis of the hollow cylinder. Because ofthe proximity of the ignition source to the region on the outside of thepore burner 4″ in which a particularly large amount of gas/air mixtureemerges, it is ensured by simple and reliable means that even a singleignition spark is sufficient to set combustion in motion. Naturally, inanother variant, the ignition source 22 mounted on the holder 36 cannaturally be arranged rotatable so that it is only brought to theoutside of pore burner 4″ in the case of ignition.

FIG. 4 shows a section of the pore burner system 3′ or pore burner 4″depicted in FIG. 3. It is apparent here that the baffle plate 100already begins in burner tube 24 and extends into the internal space ofpore burner 4″. The baffle plate 100 is preferably fastened in theregion of burner tube 24. The gas/air mixture introduced by a feed tube26 encounters the baffle plate 100 in burner tube 24 and is deflected byit partially in the direction toward the inside wall region of poreburner 4″.

FIG. 5 is a schematic cross-sectional view of the pore burner system 3′or pore burner 4″ according to FIG. 3. According to it, the baffle plate100 is arranged sloped in the same direction both in burner tube 24 andin the pore burner. For this purpose a uniform angle can be used, forexample, in the range of 20 to 25°. As is apparent from FIGS. 4 and 5,the pore burner 4″ has a groove 18 incorporated in the pore burnermaterial in the connection region with the burner tube, which is alreadysufficient to ensure reliable connection to the burner tube 24. It islikewise possible to provide a thread in the pore burner material in theregion of the outer wall, which leads to a secure connection to acounter-thread applied to the burner tube 24.

Already with the depicted baffle plate 100 a gas mixture can be guidedaccordingly so that a locally limited pressure increase occurs in theregion of the inside of the pore burner present as a hollow element.This design is also advantageous to maintain a flame in a cold burner.If necessary, a blower is provided in order to introduce the gas mixtureto the pore burner hollow element or an existing blower is equipped withincreased power, since the pressure losses are generally increased byincorporation of a baffle plate.

The features of the invention disclosed in the previous description, inthe drawings and in the claims can be essential both individually and inany combination for implementation of the invention in its differentvariants.

LIST OF REFERENCE NUMBERS

-   -   1 cooking appliance    -   2 internal space of the cooking appliance    -   3, 3′ pore burner system    -   4, 4′, 4″ pore burner    -   6 supply line    -   7, 7′ dimensionally stable molded element    -   8 base with thread    -   10 wall of hollow cylindrical molded element    -   12, 14 irregularities or grooves of the molded element    -   16 surface of the molded element    -   18 groove    -   22 ignition source    -   24 burner tube    -   26 feed tube    -   28 flange    -   34 screw holes    -   36 mount    -   100 baffle plate

1-33. (canceled)
 34. Pore burner with a housing having at least oneinlet or outlet for gas, air, and/or exhaust where the housing has atleast one dimensionally-stable porous molded element comprising at leastone of sintered metal powder and pressed metal wire mesh, the moldedelement having at least one of pore spaces in which reaction zones arepresent for flame development or a surface in which reaction zones arepresent for flame development to form a flat burner, wherein the moldedelement comprises at least one integral mounting element and/orfastening element through which at least one inlet of thedimensionally-stable molded element can be securely connected to atleast one inlet tube and/or burner tube for air and/or gas, withoutrequiring additional fastening elements.
 35. Pore burner of claim 34,comprising at least two assembled molded elements lying one against theother, at least in sections, in form-fitted fashion, which are stablyconnected to each other in at least one tongue and groove fashion andbevel and groove fashion.
 36. Pore burner of claim 34, wherein themounting and/or fastening element comprises at least one of a groove,tongue, flange, or thread.
 37. Pore burner of claim 34, wherein themolded element comprises a hollow element.
 38. Pore burner of claim 37,wherein the molded element is a hollow cylinder.
 39. Pore burner ofclaim 37, comprising at least one distribution device for deliberatealignment of part of the gas or air or gas/air mixture stream, arrangedand/or shaped at least in sections in the hollow element of the poreburner so that part of the air, gas or gas/air mixture stream can bedistributed so that an inside wall of the hollow element experiences anon-homogeneous pressure distribution.
 40. Pore burner of claim 39,wherein the non-homogeneous pressure distribution occurs in the regionof the distribution device.
 41. Pore burner of claim 39, wherein thedistribution device is a baffle plate.
 42. Pore burner of claim 41,wherein the distribution device comprises an essentially metallic and/orceramic material.
 43. Pore burner of claim 39, wherein the distributiondevice is present in sections or fully in the hollow element and/or theburner tube.
 44. Pore burner of claim 39, wherein the distributiondevice is fastened at least in sections to the burner tube and/or thehollow element.
 45. Pore burner of claim 39, wherein the distributiondevice has no direct connection to the hollow element.
 46. Pore burnerof claim 39, wherein the distribution device has a deflection surfacesloped relative to a center axis of the hollow element.
 47. Pore burnerof claim 46, wherein the distribution device is a baffle plate.
 48. Poreburner of claim 46, wherein the hollow element is a cylinder.
 49. Poreburner of claim 39, wherein a maximum cross-sectional surface of thedistribution device in a direction of flow of the gas/air mixture ismore than 50% of the cross-sectional surface of the hollow element inthe region of the distribution device.
 50. Pore burner of claim 35,wherein material densities of at least two adjacent molded elements aresubstantially equal.
 51. Pore burner of claim 50, wherein the materialdensity in the region of a connection site of two joined molded elementsis substantially equal to the material density of at least one of thesemolded elements.
 52. Pore burner of claim 34, wherein the surface of themolded element has at least one irregularity.
 53. Pore burner of claim52, wherein said irregularity encompasses at least one indentationand/or elevation that deviates from the base surface of the moldedelement.
 54. Pore burner of claim 34, wherein a wall thickness of themolded element varies.
 55. Pore burner of claim 34, wherein said poreburner is a flat flame burner.
 56. Pore burner of claim 34, wherein themolded element has a compressed density in the range of about 2.5 g/cm³to about 5 g/cm³, at least in an area.
 57. Pore burner of claim 56,wherein said compressed density is in the range of about 2.8 g/cm³ toabout 4.5 g/cm³.
 58. Pore burner of claim 56, wherein said compresseddensity is in the area of a metal wire mesh.
 59. Pore burner of claim34, wherein the process metal element comprises a compressed wire meshhaving a wire diameter being in the range of about 0.1 mm to about 0.4mm.
 60. Pore burner of claim 59, wherein the wire diameter is in therange of about 0.16 mm to about 0.28 mm.
 61. Pore burner of claim 34,wherein the porous molded element comprises a compressed wire meshincluding one to five metal wires.
 62. Pore burner of claim 61, whereinthe wire mesh includes one, two, or three metal wires.
 63. Pore burnerof claim 34, wherein the metal wire mesh is wound axially or radiallybefore pressing.
 64. Pore burner of claim 34, wherein surface loads inthe range from 200 W/cm² to 300 W/cm² are accessible with said poreburner.
 65. Pore burner of claim 64, wherein surface loads of 30 W/cm²to 260 W/cm² are accessible with said pore burner.
 66. Pore burner ofclaim 34, wherein the metal powder and/or metal wire mesh includes atleast one metal and/or metal alloy that forms an oxide layer.
 67. Poreburner of claim 66, wherein said metal alloy contains at least one ofchromium and aluminum.
 68. Pore burner system comprising a pore burnerof claim 34, an ignition device, and at least one feed tube for airand/or gas, which can be connected to an inlet of the pore burner and/orthe ignition device.
 69. Pore burner system of claim 68, wherein atleast one inlet of the dimensionally-stable molded element is connectedto at least one feed tube and/or burner tube for air and/or gas via amounting and/or fastening element.
 70. Pore burner system of claim 69,wherein said mounting and/or fastening element is a flange and/or athread.
 71. Pore burner system of claim 68, wherein the ignition deviceis arranged in the region of the outside of the hollow element at thecorresponding inside of which the distribution device has the smallestspacing.
 72. Cooking appliance comprising at least one pore burner ofclaim
 34. 73. Cooking appliance comprising a pore burner systemaccording to claim
 68. 74. Heating appliance comprising at least onepore burner of claim
 34. 75. Heating appliance comprising at least onepore burner system of claim 68.